The invention relates to a brake control valve.
There are known valves which, when actuated, initially bring operating devices to a ready position (filling stage), and which, upon further actuation, deliver the essential operating pressure to the operating devices (pressure stage). In a hydraulic brake arrangement the brake cylinder must initially be filled with hydraulic fluid until the brake cylinder makes contact with the brake disk. Only then does further pressure build-up produce the actual braking action. Accordingly, the design of a hydraulic brake system must be proportioned in such a way that the fluid volume displaced by the brake control valve cylinder (master cylinder) is sufficient to fill the brake cylinder (slave cylinder) and to force the piston of the brake cylinder into contact with the brake disk. In addition, the fluid pressure generated by the brake control valve must be sufficient to obtain the required braking action.
The fluid volume displaced may be increased by increasing the diameter and the stroke of the piston of the brake control valve, while an increase in fluid pressure requires an increase in the force applied to the brake control valve piston. However, there are limits to the design of the stroke and the applied braking force. Which stroke and which braking force can be achieved will depend upon the particular conditions. In a vehicle brake, the stroke will depend upon the maximum travel of the brake lever, which is prescribed by the optimum pedal travel. A foot-operated brake is limited by the force of the foot upon the brake pedal which must be sufficient for the desired braking force. The force on the pedal may not exceed the limit established by law.
An increased fluid pressure and therewith an increased braking action can be realized by a reduction in the diameter of the brake control valve piston, within the limits of the prescribed pedal force. However this would require an increase in the stroke of the brake control valve piston, in order to provide the required fluid volume to fill the brake cylinder. The stroke, however, is limited by the optimum pedal travel.
In the design of a brake system the pedal force, the brake lever ratio, pedal travel, brake control valve cylinder and brake cylinder must be balanced among each other. By increasing the diameter of the brake control valve cylinder the pedal travel could be reduced, assuming the pedal force remains constant, which also will reduce the resulting braking force. Corresponding problems can be encountered in the design of valves for other applications.